Hi, I think made easy answer is correct because.
For each object there will be connection establishment, object transfer and connection termination.
Total RTT for one object = 1 RTT (connection establishment) + 1 RTT (object transfer) + 1 RTT (connection termination) = 3 RTT.
As we have total 3 objects hence we will multiply the RTT for 1 object by 3 as for each object connection establishment, object transfer and connection termination is required.
Total RTT (Non- persistent ) = 3 * 3 RTT= 9 RTT.
Hence total message= 9 * 2= 18 message.
Only 1 connection establishment, 3 object transfer and 1 connection termination.
Total RTT (Non- persistent ) = 1 RTT (Connection establishment) + 3 RTT (Object Transfer) + 1 (connection transfer) = 5 RTT .
Hence total message= 5 * 2= 10 message.
So message saved in Persistent mode over non-persistent mode = 18-10= 8 messages.
Note: None of the answer here already given considers the connection termination RTTs IDK why.